1. Field of the Invention
The invention relates to a semiconductor light emitting device and a flip chip package device.
2. Description of Related Art
Light-emitting diode (LED), in comparison to conventional incandescent lamp and fluorescent lamp, has absolute advantages in environmental protection, electro-optical conversion efficiency and service life, but there still exists problems in lighting popularization and application, such as light emitting efficiency and production costs.
Light emitting efficiency of the light-emitting diode (LED) is commonly referred as external quantum efficiency of an element, which is a product of internal quantum efficiency of the element and light extraction efficiency of the element. The so-called internal quantum efficiency of the element is in fact the electro-optical conversion efficiency of the element itself, and is mainly related to the characteristics of the elements, such as energy bands, defects, and impurities of the material of the element and epitaxial composition and structure of the element. In homojunction structure, for example, probability of having an electron meeting and combining with an electron hole (producing light) is very low, viz., very low light emitting efficiency. Light extraction efficiency of the element is a number of photons at the external of the element capable of actually being detected after photons generated in the internal of the element have gone through absorption, refraction and reflection of the element itself.
Generally, internal quantum efficiency of the high quality light-emitting diode may reach 90% or more; however, when photons generated by an active layer (light emitting layer) reach a chip and air interface and have an incident angle greater than a critical angle, a total internal reflection (TIR) is to occur. In the other word, only photons smaller than the critical angle may be emitted out, while the rest of photons is reflected back into the chip. Photons inside the light-emitting diode chip, after went through multiple reflections, are finally absorbed by the materials, thus causing the loss in light extraction efficiency, thereby influencing external quantum efficiency and becoming the biggest stumbling block for enhancing the light emitting efficiency of light emitting diode.